This is a nationalization of PCT/NL00/00047, filed Jan. 21, 2000 and published in English.
The present invention relates to a loom with an insertion brake which is disposed between a yarn feeder and the shed of the loom, which insertion brake comprises a movable brake element, which is capable of movement between two fixedly disposed yarn guides from a position of rest on one side of the yarn to an operative position on the other side of the yarn, wherein the movable brake element is connected to a driving motor, the excitation of which is controlled by an electronic system, wherein at least one programme for the time and the position of the movable brake element is incorporated in said electronic system.
In looms, in particular air looms, the weft yarn is carried into the shed from a yarn feeder at a high velocity during the insertion process. Near the end of the insertion process, the yarn movement is braked abruptly by a braking element on the yarn feeder, wherein the kinetic energy contained in the weft yarn is converted into tension energy in the yarn. High tension peaks may occur in the yarn thereby, which may have various undesirable consequences and which may in some cases even lead to yarn breakage.
In order to obviate the occurrence of such a tension peak and/or damp it at least partially, EP 0 356 380 discloses a loom wherein an insertion brake is disposed between the yarn feeder and the shed of the loom, which insertion brake comprises a driven, movable brake element, which is capable of movement between two fixed yarn guides from a position of rest, wherein the yarn is not passed over the fixed yarn guides, or only to a small extent, to an operative position, wherein the yarn is passed over the yarn guides to a greater extent. The movable brake element is thereby driven in such a manner that the brake element is first moved from its position of rest to a maximum stroke position at the end of the insertion process or shortly therebefore. Then the brake element is returned from its maximum stroke position to a reduced stroke position under the influence of the reactive force of the yarn, wherein the kinetic energy contained in the yarn is reduced and the occurrence of a tension peak is obviated or at least damped. In the prior art loom all this is according to one embodiment achieved in that the movable brake element comprises an elastic part, which is pressed down by the reactive force of the yarn following a maximum stroke of the brake element, whereby kinetic energy from the yarn is stored in said elastic parts In another embodiment, the brake element is controlled by a linear magnetic motor, which is so controlled that the brake element is only moved to its maximum stroke position upon major excitation of the motor, after which the degree of excitation is reduced and the reactive force of the yarn is capable of returning the brake element against the motor force, whereby reduction of kinetic energy in the yarn takes place again, so that the tension peak is damped in this manner as well. In both embodiments an interaction between the reactive force of the yarn and a mechanical or electrical force of the brake element takes place, therefore. This interaction may lead to malfunction, especially at higher operating speeds of the loom, so that an optimum damping of the tension peak that occurs cannot be achieved.
Another embodiment of a loom of the kind to which the present invention relates is disclosed in EP 0 155 431. In this prior art loom, the brake element which is capable of movement between two fixed guides is a lever, whose movements are controlled by a cam driving unit. A position-time diagram is stored on the circumferential surface of the cam in question, according to which the movable brake element""s positions are controlled during the insertion process. Such mechanical control of the movable brake element is satisfactory per se for lower-speed looms, but one drawback is the fact that constantly the same position-time diagram is gone through for each insertion. Generally such mechanical control is not sufficiently flexible for quickly varying operating conditions, whilst it is furthermore difficult to adapt to varying yarn qualities, for example. Furthermore, this mechanical control of the brake element is fairly inelastic (rigid), so that problems may arise in case of sudden thickenings in the yarn.
In order to make a loom of the above kind more flexible and more easily adaptable to varying operating conditions, EP 0 605 531 presents a loom wherein the movable brake element is driven by a fast-response stepping motor or DC motor, which is controlled by an electronic control device, which comprises a programme section incorporating a variable programme for time and position of the brake element, at least between insertions. The connection between the motor and the brake element is inelastic thereby, and the driving force of the motor is larger than the maximum reactive force of the yarn at all times, so that it is possible to go through any position-time diagram for the brake element that may be desired. One drawback of this prior art loom is the fact that the brake element control is still rigid, so that problems may arise after all when sudden thickenings are encountered in the yarn.
From Dutch laid-open patent application No. 6712481 a yarn brake is known which comprises a stationary brake element and a movable brake element. The movable brake element is thereby driven by a moving coil motor, which is excited via an electronic system, wherein a position detection sensor is incorporated in the electronic system, which position detection sensor senses the instantaneous position of the movable brake element. The amount of current being supplied to the moving coil motor thereby depends on the position of the movable brake element as sensed by the position detection sensor, all this in such a manner that the final tension of the yarn will remain constant, also in the case of variations in the initial tension. This yarn brake is a genuine yarn tension regulating device, therefore.
Another device for regulating the yarn tension in looms is disclosed in EP 0 467 059. In this device the movable brake element is a two-armed rotary lever, one end of which is movable between two fixed yarn guides and the other end of which carries a magnet coil, which co-acts with two spaced permanent magnets of a linear electric motor. In a lever position wherein the yarn is passed over the fixed guides, said permanent magnets produce an effect like a spring. The yarn tension thereby exerts a reactive force on the lever, which is compensated by the degree of excitation of the linear electric motor. The instantaneous yarn tension is calculated on the basis of the degree of excitation of the linear electric motor. The electronic control system for the linear motor furthermore includes a position detection sensor, which continuously senses the instantaneous position of the lever. The instantaneous yarn tension calculated from the degree of excitation of the linear motor is compared with a desired yarn tension for each position, and in case of a deviation the degree of excitation of the linear motor is changed. Thus the yarn tension can be regulated in such a manner that it conforms to a specific desired position-tension diagram. Furthermore the linear motor of this prior art device can also be excited in such a manner that the brake element takes up positions which are required for drawing back the yarn at the end of the insertion process.
The object of the present invention is to provide a loom wherein the movable brake element is controlled in a flexible and very precise manner whilst exhibiting sufficient elasticity to be able to cope with sudden variations in the yarn quality or the yarn thickness.
In order to accomplish that objective, the loom according to the invention is characterized in that the electronic system comprises a position detection sensor for sensing the instantaneous position of the brake element, wherein the electronic system compares the instantaneous brake element position with the position which is desired according to the programme and, if a deviation is established between the sensed instantaneous position and the desired position, controls the amount of current being supplied to the motor in such a manner that said deviation is at least largely eliminated in cooperation with the reactive force of the yarn.
The brake element used in the loom according to the invention can be driven by any type of electric motor, wherein the force to be exerted by the motor upon movement in the direction of its maximum stroke position only needs to be a little larger than the reactive force exerted by the yarn, whilst the motor force may even be smaller than the reactive force of the yarn upon return of the brake element from its maximum stroke position, whereby the reactive force of the yarn causes the brake element to move back. Possibly, a negative motor force can be employed, if desired, so that the return movement of the brake element is not only the result of the reactive force of the yarn, but it is also assisted by the motor. As a result, the return movement of the brake element will take place at a higher velocity. The electronic system controls the motor force in such a manner that the brake element position sensed by the sensor is compared continuously or at intervals with the position as desired by the programme, and in that the motor force is so controlled in case of a deviation that this deviation is eliminated. In this manner the desired position-time diagram of the movable brake element is followed precisely, whilst the brake element is not controlled in an undesirable, rigid manner. Sudden thickenings that may occur in the yarn can effect an instantaneous movement of the brake element, with a deviation occurring between the desired position and the instantaneous position, which deviation is subsequently eliminated. Yarn breakage will be rare.
Any suitable type of motor, for example a hydraulic, pneumatic or electric motor, can be used for driving the brake element.
According to another embodiment, the movable brake element is made up of one end of a lever which is rotatable about a shaft, wherein said shaft is linked to a rotary solenoid motor. The advantage of such a motor is its low moment of mass inertia and short response time.
Another advantageous embodiment, wherein the movable brake element is moved from its position of rest to its maximum stroke position shortly before the end of the insertion process, is characterized in that the electronic system excites the driving motor sooner and/or more strongly as the end of the insertion process comes earlier, so that the maximum stroke position is reached more quickly. In this manner it is achieved that the maximum stroke position is reached sooner at higher yarn speeds, so that the reduction of the kinetic energy contained in the yarn is initiated sooner, so that the feared tension peak will be damped in time and to a sufficient degree at higher yarn speeds as well. The use of a yarn winding counter on the yarn feeder makes it possible to count the number of windings being unwound from the yarn feeder, wherein, when detection of a predetermined number of windings being reached before the end of the insertion process causes the electronic system to excite the movable brake element. In this manner it is possible during the insertion process already to adjust the moment of driving of the brake element to the fact that the end of the insertion process will be reached sooner or later.
Another advantageous embodiment of the loom according to the invention is characterized in that the mass inertia of the movable brake has been selected to be so low that the force being exerted on the brake element is capable of moving the brake element upon detection of irregularities in the yarn. It is noted that the term mass inertia of the movable brake element is to be understood to mean the mass inertia of the brake element itself and also of all the parts connected thereto. In this manner it is achieved that a thickening that may occur in the yarn will be capable of moving the brake element when it strikes against said brake element, which movement will be sensed by the position detection sensor, after which the control system will directly eliminate the deviation between the desired position and the instantaneous position. A thickening or other yarn irregularity can thus pass the brake element practically without impediment, without this leading to impermissibly high tension peaks in the yarn.
In looms comprising insertion brakes of the kind to which the present invention relates, the position detection sensor produces an electric signal of a specific magnitude for every current position of the brake element. The control system recognises these electric signals as a measure of a specific current position of the brake element. This means, therefore, that an electric sensor signal of one specific magnitude is associated with every current position of the brake element. A problem which occurs thereby is that the sensors that are used may exhibit a certain deviation in the magnitude of the signals they generate. This might lead to one sensor generating a signal of a different magnitude than another sensor in one specific current position of the brake element, therefore, causing the control system to derive therefrom a position which does not exactly correspond to the current position of the brake element. In order to overcome this problem, another embodiment of the insertion brake according to the invention is characterized in that the movable brake element is capable of movement between a first stop and a second stop, and in that the electronic system includes a control module for adjusting the position detection sensor, wherein the control module first stores a first signal from the position detection sensor when the brake element abuts against said first stop, and then records a second signal when the brake element abuts against said second stop, storing the difference between said first and said second signal as a maximum (100%) value of the path through which the brake element can travel, after which the module in use converts the signals from the sensor associated with the instantaneous positions of the brake element to a percentage of said difference signal, from which the instantaneous position of the brake element follows as a percentage, of the maximum stroke position of the brake element, which momentary position is compared with the desired position by the electronic system.
When the insertion brake is placed into service or when the sensor is replaced, the brake is first moved to a position wherein it abuts against the first stop (minimum stroke position), after which the first signal delivered by the position detection sensor is recorded by the control module. Then the brake is moved to a position wherein the brake element abuts against the second position and the second signal delivered by the position detection sensor is recorded again. The control module then determines the difference between the first and the second signal, which difference will be a measure for the spacing between the first and the second stop.
Following that, the brake can be placed into service. In a specific position of the brake element, the position detection sensor will now deliver a signal which is related to the stored difference signal in the control module and which is converted into a percentage of said difference signal. Accordingly, this percentage is also a percentage of the difference between the minimum (abutment against the first stop) and the maximum (abutment against the second stop) position of the brake element. In this manner reliable information as to the instantaneous position is obtained.
The position detection sensors can thus be adjusted easily and quickly before being placed into service, so that any differences in their operation will not effect the further control system of the brake.
It is noted that the brake element is only brought into contact with the said two stops when the sensor is being adjusted. During the further operation of the brake, the brake element will move within an range of 20-80% of the maximum stroke position between said stops.
In order to be able to verify whether a specific insertion brake is still functioning sufficiently quickly and accurately after some time, a further embodiment of the movable brake element is arranged for verifying whether the movable brake element has completed a specific position change within a specific period of time with a predetermined degree of excitation. For example, it is possible to verify therewith whether the brake element has completed a position change of 50-80% within a specific period of time with a predetermined degree of excitation. This verification preferably takes place in a range of movement of the brake element in which there will be no influencing by the yarn. Thus it is possible to establish in a simple manner whether the friction has so increased, for example due to fouling or otherwise, that the insertion brake no longer meets the requirements made thereof.